Soils as a factor in pinyon pine mortality due to ips beetle infestation in Garden Park, Colorado: A case study

Observations by European settlers indicate that the distribution of pinyon - juniper woodlands has been expanding in the southwestern United States over the last two centuries. Beginning in the late 1990s, drought conditions in the region, along with ips beetle infestations have led to destruction of entire viewsheds of pinyon pine trees. The reduced availability of moisture associated with drought stresses pinyon pines and reduces their ability to resist ips beetle infestation. They are unable to produce the sap necessary to pitch out the boring beetles. These woodlands exist on a marginal environment where slight variations in the moisture balance affect the survivability of such trees. Factors such as elevation, slope, aspect, tree density and soil properties affect the moisture availability of the trees. This study looks at the nature of soil as a possible factor in a tree's ability to resist ips beetle infestation. Trees situated on deeper, richer soils with greater water holding capacity and shallower slope were expected to show an increased resistance to ips beetle infestation. The results of this research, however, did not show any statistically significant difference between the soil conditions at infested and uninfected sites. This finding leads to speculation that after some as of yet unknown point in a drought cycle, even those trees on the best soils are susceptible to beetle infestation and cannot survive.